Over time, the quality of various fuels can degrade. Color quality is one characteristic of a fuel that can degrade over time during storage. Thermal oxidation stability is another.
Robert N. Hazlett, “Thermal Oxidation Stability of Aviation Turbine Fuels,” ASTM Publication Code Number 31-001092-12, 1991, reports a process that was considered effective in improving jet fuel thermal oxidation stability.
Schwartz, F. G., and Eccleston, B. H., “Survey of Research on Thermal Stability of Petroleum Jet Fuels,” BuMines Information Circular 8140, Bureau of Mines, Washington, D.C., 1962, reports that sulfur dioxide (SO2) extraction, acid treating, and absorption methods improve the thermal stability of jet fuel. with sulfuric acid, caustic, or SO2 have waste disposal problems. The use of absorption methods with agents such as silica gel or alumina have met with marginal success. Clay adsorption generally requires large quantities of material.
Statutory Invention Registration No. U.S. H1368 describes a method for improving the long-term color stability of jet fuel and jet fuel blends containing nitrogen compounds by intimately mixing the jet fuel with a quantity of concentrated sulfuric acid sufficient to remove at least 90% of the nitrogen compounds during contact time equal to or less than 5 minutes; separating the jet fuel from the concentrated sulfuric acid; mixing the jet fuel with an aqueous caustic solution to remove residual acid from the jet fuel; separating the jet fuel from the aqueous caustic solution; mixing the jet fuel with water; and separating the jet fuel from the water.
U.S. Pat. No. 4,912,873 relates to the treatment of diesel or jet fuel with a non-ionic, macro-reticular, cross-linked, acrylic aliphatic ester resin such as XAD-7 that reduces polar impurities and diesel color. The diesel or jet fuel samples are analyzed by the “floc test” which measures the amount of floc visually observed on contact with an aqueous iron solution containing 5 mM ferric sulfate in 5 mM sulfuric acid.
U.S. Pat. No. 2,267,458 relates to a process for refining hydrocarbon oil containing objectionable sulfur, color, and gum-forming compounds. The process comprises subjecting the oil to treatment with used sulfuric acid, which has been obtained from the alkylation of isoparaffins with olefins in the presence of strong sulfuric acid, whereby such objectionable compounds are substantially removed.
U.S. Pat. No. 3,487,012 relates to a process for the improvement of initial color and long-term color stability of aromatic concentrates. The process is considered to improve both initial color and long-term color stability of aromatic concentrates boiling between 400 to 750° F. without substantially reducing the aromaticity. The process comprises hydrotreating, acid treating followed by caustic washing, and vacuum distilling the aromatic concentrates at 5-250 mmHg absolute pressure with corresponding temperatures from 150° F. to 650° F.
Additional methods of enhancing color quality and stability of fuels are needed. In particular, more simple processes using more readily available materials as catalysts to assist in such processing are highly desired.